the idea is that nigger jim is what everyone else called him while jim is his name twain doesnt hold the same opinion as the characters in his world do these characters in the narrative however are racist when out of narrative so in talks about the book et cetera he used the phrase for the following reason the people whom huck and nigger jim encounter on the mississippi are drunkards murderers bullies swindlers lynchers thieves liars mows frauds child abusers numbskulls hypocrites windbags and traders in human flesh all are white the one man of honor in this phantasmagoria is nigger jim as twain called him to emphasize the irony of a society in which the only true gentleman was held beneath contempt quoted directly from the wikipedia page